Like a lot of cult rock artists, Stephen Duffy keeps an online blog. It usually contains the sort of things that you would expect to find in a cult rock artist's online blog: recommendations of albums and books, wry acknowledgments of the activities of his small-but-rabid worldwide fanbase, news of limited-edition seven-inch singles by the Lilac Time, the glorious folk-rock band he formed with his brother Nick in the mid-80s, and which split up in 1991, then reconvened eight years later.

In recent weeks, however, Duffy's blog has taken on a noticeably different tone: one part bemusement to two parts excitement. There have been reports of writing sessions in LA. There was a substantial disquisition on finding a suitable outfit for Top of the Pops: "I looked at clothes, but as I am not a gay teenager couldn't find anything." Most recently, there was a description of sitting through CD:UK, waiting for confirmation that Radio, the single he has written and produced with Robbie Williams, had entered the charts at No 1.

Two days after Cat Deeley's happy announcement, the aura of slightly bemused excitement is still intact as Stephen Duffy sits in a pub near London Bridge: "I've never been No 1 anywhere apart from Iceland," he smiles, "and I think they say that to everyone."

His conversation is an intriguing combination of dry self-deprecation and bullish confidence. On the one hand, blessed with a sense of timing that would shame a stand-up comedian, he has a tendency to end anecdotes with a punchline that usually revolves around the failure of one or other of his albums to transform lavish critical acclaim into world-beating sales.

The Lilac Time's last three records are his favourites, he says, because they "were made for myself, without record company involvement and with nobody trying to sell them". A beat. "And nobody trying to buy them either." He flirted with Britpop in the mid-90s, releasing two albums under the name Duffy and scoring a minor hit with Me Me Me, also featuring Blur's Alex James and Elastica's Justin Welch, but it all came to an abrupt end: "It was, 'come back to England, everyone's going to get a record deal.'" A beat. "'Oh hang on, everybody except you.'"

On the other hand, he listened to the Radio 1 chart countdown on Sunday, and when they got to Radio, he was astonished: "It made me realise how different it was, not just from previous Robbie Williams singles, but from everything else in the chart. It's like screaming from some far-off planet where music is still interesting."

He is full of praise for the apparently effortless songwriting skill of his new collaborator: "Have you seen that bit in Eat the Document where Bob Dylan and Robbie Robertson are sitting on a bed writing a song and this stream of consciousness is just coming out? He does that. He played the bass synthesizer on Radio. He co-produced it. He's just about the only person of his generation that's doing that. 'Robbie Williams makes his own records.' I'm surprised that's not the front page of the newspaper."

He is equally surprised that said newspapers are once more referring to him as Stephen "TinTin" Duffy, the flatly awful name he adopted during his own flirtation with the Top 10 19 years ago. "You forget that life goes on, that people have lives and work, and that you have to be in the Top 10 for it to be in their world. I forgot about that because I've been making music, without thinking about the charts. People go, 'Do you remember him?'" A beat. "'I don't remember him.'"

Rather annoyingly, he still looks like him: at 44, Duffy's face bears a remarkable resemblance to the one staring imperiously from somewhere between a designer suit and a quiff on the cover of his 1985 debut album, The Ups and Downs. He says that he was never terribly comfortable as a pop star. He famously formed Duran Duran while at art school, but left after four gigs. He had intended to pursue a Dylan and Stones-inspired band called Obviously Five Believers, but nobody was interested in 1982. "All my friends had been on Top of the Pops and I was freaking out: "'I'm 22 and I haven't been on Top of the Pops yet!' I redid the songs on a synthesizer and it took me about five minutes to get a deal. I was cynical about how I got the record deal. I was cynical about the music I was making because I knew it wasn't as good as punk."

Perhaps understandably, his tenure as a teen idol was brief and marked by a series of deliberately abstruse career moves. He unsuccessfully lobbied to release a Dixieland jazz track as the follow-up to his second hit, Icing on the Cake. He publicly lauded the folk music of his childhood, proselytising to bewildered Smash Hits interviewers about the Incredible String Band and Nick Drake: you didn't get that sort of thing from Go West. He was an early adopter of ecstasy, and put out an album under the name Dr Calculus MDMA, which presumably seemed a subtle pun in the more innocent pre-acid house climate: "It was an attempt to soundtrack the experience. Before you realised that acid house was going to be such a narrow church, I thought it could be anything. So let's make a psychedelic record with a trombone on it," - a beat - "which is obviously a recipe for success in any era."

His record company finally cracked when he announced his intention to form the Lilac Time in 1986. The band never had a hit single - "which was surprising, because we did the Roland Rat show, which we thought was going to catapult us into the hearts of teenage Britain" - but their wistful acoustic balladry began to sound remarkably prescient when Britpop foundered and the cult of the singer-songwriter returned with a vengeance.

Williams was a fan of their 1999 album Looking for a Day in the Night: he first co-opted the band's vocalist Claire Worrall, then approached Duffy, who was won over by the singer's unlikely tastes in music - "he has an in-depth knowledge of New Order and Joy Division, and a real appreciation of Morrissey" - and desire to musically reinvent himself. "This is not a career move," Duffy insists. "People have come to see me about writing with them before, but when I've asked them what they want to do, they had no idea, so nothing happened. But Rob wants to be different, and I don't want to be the same. I don't want to make a Lilac Time record with someone else singing."

Indeed, he may not make another Lilac Time record for the foreseeable future, much to the chagrin of rock critics and a small-but-devoted worldwide fanbase. There just isn't the time: the partnership with Williams has thus far yielded 60 songs, "all types of experimentation" and an album due for completion next year: "I'm really enjoying it. I don't see why I should stop."

Indeed, Radio's success comes with only one reservation. "You're supposed to do in the second half of your life what you didn't do in the first," he muses, and I'm failing miserably. I'm back on Top of the Pops."

Has it changed?

"Not really. They still do that wavy arm thing if you play a slow song. And there's never anyone interesting on." A beat. "Apart from me. Or Robbie Williams."